The difference in testosterone levels between males and females is large. The normal range of testosterone in adult males is 14 to 25.4 nmol/L, and the normal range of testosterone in adult females is 1.3 to 2.8 nmol/L; in childhood, the testosterone level is a bit lower than in adulthood. Testosterone is important for men to maintain secondary sexual characteristics, libido and normal sexual function; when men are overweight, viral or bacterial infections affect testicular function, and the hypothalamic-pituitary-gonadal axis is impaired, this can lead to a decrease in testosterone levels, as well as certain medications that may cause a decrease in testosterone levels, such as finasteride. For women, an abnormally high testosterone level should alert them to the presence of polycystic ovary syndrome. In addition to this, abnormal adrenal function, or oral androgenic medications may also lead to elevated testosterone levels. Patients should not rely on a single test result to determine a particular disease, and are advised to visit a hospital and work with a physician for further treatment.